Am I making a mistake?

So I (31 f) have been with my boyfriend (35m) for around 5 years. We’ve been thru a lot in these years and there have been unfaithful moments (on both ends) but we’ve stayed together and worked on the issues we have and I feel like we’re in a great place in our relationship now.

On Valentine’s Day I went thru his phone while he was asleep and found him talking to multiple women. One of which he worked with. I read through some of their messages, went to the shared pics to see what they’ve sent each other and found nudes. I called her from his phone that night and she’s still terrified 😅Long story short; we ended up staying together and the girls had transferred to a different location.

Here’s my dilemma.. I want a woman in my face. And I don’t want to cheat on him so I want to find somebody to join us. We’ve been in our hometown for the weekend so you would think it would be easier where you know people but no it’s worse lol. So anyways last night while he and I were doing drugs and trying to find a girl to share I text her just to engage conversation and see where her head was at as far as him. She admitted she still has feelings and still initiates contact but she also said he doesn’t respond most of the time. So he and I have already talked about including somebody (possibly her it was not too long after the phone incident) but I’m not sure if I want to open that can of worms back up so to say… he’s a completely different man than he was before I went through his phone and he tries to please me and make me happy in every way. Should I fulfill both of our fantasies or should I wait and look for somebody else?

I’ve been talking to her all day and we plan to meet today to see if we can even vibe together.. she’s been flirting with me and I kinda wanna see where this will go but also don’t want to lose the relationship I have with my partner now..

TLDR; Should I have a threesome with my boyfriend and the side chick I found out about?